BUBBLES IN A LIQUID CARRIER

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.

62/714,279, filed on August 3, 2018, the contents of which are hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates to expanding nano-bubbles dispersed in a liquid carrier.

BACKGROUND

Dissolved air flotation systems have been used to remove contaminants, e.g., oils and solids, from liquids such as wastewater. In a dissolved air flotation system, a gas is dissolved in the liquid under pressure. The pressure is then lowered, thereby forming micro-bubbles that can float to the surface of the liquid. The bubbles adhere to the contaminants and float to the surface of the liquid, where they can be removed, e.g., by skimming.

One disadvantage of dissolved air flotation systems is that pressurizing the liquid to dissolve the gas requires specialized equipment such as pressurizing water tanks or sophisticated pumps. Moreover, pressurizing the liquid to create the micro bubbles is an energy-intensive operation, which adds to cost.

Nano-bubbles have several unique properties such as long lifetime in liquid due to their negatively charged surfaces. Nano-bubbles also have high gas solubility into the liquid due to their high internal pressure, which typically is more than five times greater than atmospheric pressure. Consequently, the nano-bubbles do not rise to the surface of the liquid.

SUMMARY

There is a described an apparatus for producing a composition comprising micro-bubbles in a liquid carrier. The apparatus includes (a) a nano-bubble generating apparatus capable of creating a first composition comprising nano-bubbles dispersed in a liquid carrier; and (b) a nano-bubble expander located downstream of the nano-bubble generating apparatus. The nano-bubble expander includes (i) an l input end for receiving the first composition; (ii) a discharge end; and (iii) a chamber in communication with the input end and discharge end. The chamber is configured to reduce the pressure exerted on the first composition relative to the pressure exerted on the first composition upon introduction to the nano-bubble expander at the input end, thereby causing the nano-bubbles to expand and form a second composition comprising micro-bubbles in a liquid carrier.

As used herein, the term“nano-bubble” refers to a bubble that has a diameter of less than one micron. A micro-bubble, which is larger than a nano-bubble, is a bubble that has a diameter greater than or equal to one micron and smaller than 50 microns. A macro-bubble is a bubble that has a diameter greater than or equal to 50 microns.

In some embodiments, the nano-bubble generating apparatus includes (a) an elongate housing comprising a first end and a second end, the housing defining a liquid inlet, a liquid outlet, and an interior cavity adapted for receiving the liquid carrier from a liquid source; and (b) a gas-permeable member (e.g., a ceramic filter) at least partially disposed within the interior cavity of the housing.

The gas-permeable member includes an open end adapted for receiving a pressurized gas (e.g., nitrogen or oxygen) from a gas source, a closed end, and a porous sidewall extending between the open and closed ends having a mean pore size no greater than 1.0 pm. The gas-permeable member defines an inner surface, an outer surface, and a lumen.

The liquid inlet of the housing is arranged to introduce the liquid carrier from the liquid source into the interior cavity of the housing, typically at an angle that is generally orthogonal to the outer surface of the gas permeable member. The housing and gas-permeable member are configured such that pressurized gas introduced into the lumen of the gas-permeable member is forced through the porous sidewall of the gas-permeable member and onto the outer surface of the gas permeable member in the form of nano-bubbles as the liquid carrier from the liquid source flows parallel to the outer surface of the gas-permeable member from the liquid inlet to the liquid outlet, forming a composition that includes the liquid carrier and the nano-bubbles dispersed therein. In some embodiments, the nano-bubbles have a mean diameter less than 500 nm or less than 200 nm, or ranging from about 10 nm to about 500 nm (e.g., from about 75 nm to about 200 nm). The concentration of nano-bubbles in the liquid carrier at the liquid outlet may be at least 1 x 10 ⁶ nano-bubbles/ml, at least 1 x 10 ⁷ nano-bubbles/ml, or at least 1 x 10 ⁸ nano-bubbles/ml.

In some embodiments, gas is selected from the group consisting of air, oxygen, carbon dioxide, nitrogen, hydrogen, and combinations thereof. The liquid carrier may include water.

In some embodiments, the nano-bubble expander is in the form of a nozzle, e.g., a Venturi nozzle. The nano-bubble expander may include one or more ports disposed around the circumference of the chamber that, when the nano-bubble expander is placed in communication with a body of liquid, are capable of pulling liquid from the body of liquid into the chamber of the nano-bubble expander. In some embodiments, the ports have a generally conical cross-section and are disposed at an angle offset from the direction perpendicular to the direction of flow through the chamber of the nano-bubble expander. In some embodiments, the nano-bubble expander may be provided with a diffuser in communication with the discharge end of the nano-bubbler expander, the diffuser including a plurality of openings through which the second composition comprising micro-bubbles in a liquid carrier is discharged.

There is also described a method for producing a composition comprising micro-bubbles in a liquid carrier using the above-described apparatus. The composition may be discharged into a body of liquid.

The apparatus and method offer a number of advantages. For example, the nano-bubble generator is capable of producing a high concentration of nano-bubbles in a liquid carrier. The nano-bubbles are then expanded without adding gas to create a high concentration of micro-bubbles, which can then float. The operation may be conducted at ambient pressure, thereby eliminating the need to pressurize the liquid.

The details of one or more embodiments of the invention are set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing illustrating an embodiment of the invention in which a nano-bubble expander is positioned downstream of a nano-bubble generator.

FIG. 2 is a cross-sectional view of a nano-bubble expander in the form of a Venturi nozzle. FIG. 3 is a perspective view of a nano-bubble expander in the form of a Venturi nozzle equipped with a diffuser.

FIG. 4 is a cross-sectional view of the nano-bubble expander and diffuser shown in FIG. 3. DETAILED DESCRIPTION

FIG. 1 illustrates an apparatus 10 for generating micro-bubbles that includes a nano-bubble generator 12 and a nano-bubble expander 14 located downstream of nano-bubble generator 12. Nano-bubble generator 12 is described in the Summary, above. An example of a suitable nano-bubble generator 12 is the apparatus described in USSN 15/456,077 filed March 10, 2017 and entitled“Compositions Containing Nano-Bubbles in a Liquid Carrier,” which is assigned to the same assignee as the present application and incorporated by reference in its entirety. Nano-bubble generator 12 produces nano-bubbles in a liquid carrier, typically an aqueous carrier. The gas in the nano-bubble is selected based upon the end use of the micro-bubbles. Typical examples include air, oxygen, carbon dioxide, nitrogen, hydrogen, and combinations thereof.

Nano-bubble generator 12 outputs the nano-bubble containing composition to nano-bubble expander 14 located downstream of nano-bubble generator 12. The precise location depends upon the end use of the micro-bubbles produced by nano- bubble expander 14. As shown in FIG. 1, nano-bubble expander 14 is in

communication with a tank 16, e.g., a flotation tank. The nano-bubble expander 14 can be located partially inside tank 16, partially outside tank 16, or outside tank 16. The nano-bubble expander 14 expands the nano-bubbles and discharges them into tank 16. In the case of a flotation tank containing wastewater, the micro-bubbles adhere to contaminants such as oil and solids on the wastewater, and float to the surface of the liquid, where they can be removed, e.g., by skimming. At least a portion of the purified wastewater can then be returned to nano-bubble generator 12 for use as the carrier liquid.

Referring to FIG. 2, nano-bubble expander 14 is shown in the form of a Venturi nozzle. Expander 14 includes an input end 18 that receives the nano-bubble containing composition from nano-bubble generator 12 and a discharge end 20 that discharges the micro-bubble containing composition produced by expander 14, e.g., into a tank such as flotation tank 16. Input end 18 and discharge end 20 are separated by a chamber 22 through which the nano-bubble containing composition flows.

Chamber 22 forms a pressure reduction zone that includes a conical portion 24 that tapers to a section 26 having a reduced diameter relative to the diameter of input end 18. As the nano-bubble containing composition flows through the pressure reduction zone, the external pressure on the composition, including the nano-bubbles, decreases, thereby causing the nano-bubbles to expand and form micro-bubbles.

Nano-bubble expander 14 preferably includes one or more conically shaped ports 28 and 30 positioned at an offset angle from perpendicular relative to the direction of flow through expander 14, and arranged around the circumference of the discharge end 20. One or more rings of ports may be included. When expander 14 discharges the micro-bubble containing composition in a body of liquid, e.g., wastewater in tank 16, liquid from tank 16 is pulled into expander 14 through ports 28 and 30. This, in turn, reduces shear at the interface between discharge end 20 and the liquid in tank 16, thereby facilitating mixing and enhancing flotation efficiency.

FIGS. 3 and 4 depict an alternative design for reducing shear when the micro bubble containing composition is discharged from nano-bubble expander 14 into a body of liquid. As shown in FIGS. 3 and 4, nano-bubble expander 14 is equipped at the discharge end with a diffuser 32. Diffuser 32 includes a plurality of openings 34 and 36, and a cap 38. The micro-bubble containing composition formed by nano bubble expander 14 is discharged through openings 34 and 36 into a body of liquid. Diffuser 32 reduces the velocity of the micro-bubble containing composition as it is discharged into the surrounding body of liquid, thereby reducing shear, facilitating mixing, and enhancing flotation efficiency.

In FIGS. 3 and 4, openings 34 and 36 are shown in the form of slots parallel to the axes of diffuser 32 and nano-bubble expander 14. However, other shapes and/or arrangements may be used. For example, the openings may be spherical. Rather than arranged parallel to the axes of diffuser 32 and nano-bubble expander 14, the openings may be arranged perpendicular to the axes.

The combination of nano-bubble generator 12 and nano-bubble expander 14 finds application in a number of areas. One example, described above, is wastewater treatment in which the micro-bubbles discharged from expander 14 into flotation tank 16 adhere to contaminants and then rise to the surface, enabling removal of the contaminants. Other applications include those in which it is desirable to remove the nano bubbles at some point in the process. For example, the nano-bubbles could be used to maximize gas transfer efficiency into a fluid where the gas is high cost, hazardous, or changes the fluid through chemical reactions. After treatment with the gas, the nano- bubbles could be transformed into micro-bubbles using expander 14 to remove them from the liquid.

A number of embodiments of the invention have been described.

Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other

embodiments are within the scope of the following claims.